Optoelectronic sensors have been used for some time in the sector of industrial automation, packaging machines or food industry to detect a feature of an object.
Different types of optoelectronic sensors exist, each type being specialised in a specific application or for detecting a specific feature of an object positioned within a range of operating distances. For example, optoelectronic sensors are known that are able to detect the presence of an object and/or the colour thereof. Other types of sensor are known for detecting light areas in an object and/or for detecting the presence of an object within a preset operating “field”.
One or more operating parameters are associable with each sensor and determine the functions thereof, in the sense that the value of each parameter determines the behaviour of the sensor during a work step. Nevertheless, it is not often possible to preset the value of such parameters at the moment of production of the sensor because adjusting some of them depends on the particular mode of use of the sensor in the application of interest. Accordingly, each installation of the sensor is typically preceded by an adjusting procedure performed by an operator, by means of which the value of one or more parameters for the specific application is set.
By way of example, let us consider an optoelectronic sensor, which is typically called a “background suppressor”, is able to detect the presence of an object inside a measuring “field” that is usually used to detect the presence of an object conveyed on transport chains or on conveyor belts. The measuring field is a range of preset distances comprised between the background suppressor device and a preset limit distance (also called the cut-off distance), beyond which the presence of any object is ignored, which thus becomes part of the “background”. At the output, the sensor supplies an information signal indicating the presence or absence of an object within the cut-off distance. The cut-off distance is not in general presettable a priori but is an operating parameter regulated by an operator during installation of the sensor in relation to the position in which the background is located, which may, for example, comprise a wall of the conveyor or the conveyor itself.
The output information signal that the sensor provides is a digital signal that may assume a high or low logic status to indicate respectively the presence or absence of the object. If the sensor is set to a mode defined as “light” the information signal is a normally low digital signal that switches and becomes high in the presence of the object. On the other hand, if the sensor is set to “dark” mode the information signal is a normally high digital signal that switches and becomes low in the presence of the object. Similarly to the cut-off distance, the “light” or “dark” mode is a further operating parameter that is modifiable by the operator to define the activating logic status of the information signal.
FIG. 1 shows an optoelectronic sensor 1, in particular a background suppression sensor, according to the prior art. In order to enable the cut-off distance and the light/dark mode to be adjusted, a face of head 2 of the sensor acts as an operator panel and comprises interface means to interface an operator with the sensor. The interface means comprises indicator means, which are typically made by means of a green LED 3 and a yellow LED 4, which are suitable for indicating to an operator respectively the presence of power supply and the active logic state of the output. The yellow LED 4 lights up if the digital information signal is active and thus in the presence of the object.
The interface means further comprises adjusting means made by trimmers, proved with a slit so as to be able to be rotated by screwdriver. A trimmer is an adjustable resistive divider that provide an output voltage that is proportional to the position of an actuating shaft. Both two-position monoturn trimmers and multiturn trimmers are known, which permit several rotations of the actuator shaft up to a maximum number of possible revolutions.
In the case of the background suppression sensor shown in FIG. 1, the adjusting means comprises a multiturn trimmer 5 for adjusting the cut-off distance, and a two position light/dark trimmer for configuring the information signal. Means for controlling the sensor is connected to the adjusting means and to the indicating means, to store the parameters set by means of the cut/off trimmer 5 and the light/dark trimmer 5 and for managing LEDs 3 and 4.
A bottom face 7 of the sensor is provided with connector means 8 for connecting and integrating the sensor 1 with an external automation and/or control system (not shown), that is able to receive the output information signal supplied by the sensor 1 and to configure the sensor 1 appropriately if requested.
Although what has been disclosed before relates to a background suppression sensor, interface means comprising trimmer adjusting means is found in many types of optoelectronic sensors. If it is necessary to adjust the parameters in which the settable value is comprised in a range of possible values, knob multiturn trimmers have been used above all.
Nevertheless, the presence of multiturn trimmers in an optoelectronic sensor poses certain problems.
First of all, the number of revolutions of the trimmer and the number of adjusting ranges for each revolution determines the adjusting sensitivity of the trimmer, given by the number of revolutions multiplied by the adjusting ranges for each revolution.
In the case of parameters whose values are variable in a large range and considering the high-performance multiturn trimmers currently on the market, i.e. with the maximum number of revolutions, it is often not possible to set the value of a parameter with the required sensitivity.
Further, the higher the number of possible revolutions in a trimmer, the greater are the cost and dimensions of the trimmer. The dimension of the trimmer imposes constructional constraints on the optoelectronic sensor and this is often translated into an undesired increase in the dimensions of the optoelectronic sensor. The limited dimensions in fact make the sensor very appreciated commercially and this is valid for all the types of optoelectronic sensors.
Alternatively, in order to obtain an adjustment of a parameter in a large range, it is possible to provide the optoelectronic sensor of two multiturn trimmers of medium performance, a first trimmer intended for low sensitivity variations and a second intended for high sensitivity variations. Again, a solution of this type involves high costs and imposes constructional constraints on the optoelectronic sensor. A dual knob interface is in fact necessary and an external container of dimensions that are suitable for housing the body of the two trimmers.
From what has been said before it follows that for each type of optoelectronic sensor, or also for each model of sensor with particular technical features, a specific design is necessary to equip the model with the most suitable multiturn trimmer whilst taking account of production costs and ensuring limited dimensions. In the case of a company manufacturing different types of optoelectronic sensors, the need for this design implies a cost increase not only in terms of human resources used but also type of componentry required in the warehouse. In other words, it is almost impossible to have standard componentry in order to achieve economies of scale.
A further problem of optoelectronic sensors is linked to the number of visual indicators present in the face of the sensor acting as an operator panel. Some types of sensor in fact, or some specific applications thereof, would require additional visual indicators to indicate specific use configurations. A solution of this type not only requires the visual indicators to be multiplied, with a consequent increase of costs, but also requires the sensor to be modified over time if a new sensor function has been identified with which no corresponding visual indicator has yet been associated. In addition, the multiplication of the visual indicators is not often possible in an optoelectronic sensor, especially if there are knobs of monoturn or multiturn trimmers present, inasmuch as the dimensions of the face with the function of operator panel would increase in an undesired manner.